As used herein, "acrylic adhesives" includes methacrylic, acrylate and methacrylate adhesives. Two-component, reactive acrylic adhesives are frequently used for fabrication of plastic and metal assemblies in marine, transportation, and various other industrial applications. These adhesives offer structural bond strength, fast set time, and good resistance to temperature extremes. Acrylic adhesives, particularly methacrylate adhesives, are known in the art, which art is incorporated herein by reference; see for example U.S. Pat. Nos. 4,536,546; 4,714,730; 4,942,201 and the patents cited therein, the contents of all of which are incorporated herein by reference. Some drawbacks to using reactive acrylic and methacrylate adhesives are related to their use and cure characteristics. Acrylic adhesives, particularly methacrylate adhesives, are volatile; methacrylate adhesives are based on methyl methacrylate and other volatile methacrylate monomers. Surface evaporation of dispensed acrylic adhesives thus eventually form a dry film which results in reduced open time. Another drawback relates to the heat evolved (i.e. exotherm) while the adhesive sets or cures. Highly exothermic adhesives can distort heat sensitive substrates, such as fiber-reinforced polyester (FRP) and numerous thermoplastics. A third drawback of acrylic adhesives, particularly methacrylate adhesives, is reduced shelf-life compared to other structural adhesives like epoxies and polyurethanes. Unlike epoxies or polyurethanes, methacrylate adhesives cure by free-radical polymerization preferably initiated by certain peroxide initiators (e.g. cumene hydroperoxide or benzoyl peroxide). Since peroxides degrade more rapidly than the curing agents of epoxy or urethane technology, acrylic and methacrylate adhesives tend to be less stable.
There is a need for acrylic adhesives, particularly acrylate and methacrylate adhesives, which have longer open time and lower maximum or peak exotherm temperatures. The present invention discloses the use of inventive retarding additives which provide such improved acrylic, particularly methacrylate, adhesives.